The present invention is an improvement on the Gifford-McMahon cycle. Familiarity with said cycle is assumed. Representative prior art patents teaching such cycle include U.S. Pat. Nos. 2,966,035; 3,188,818; 3,218,815; and 4,305,741.
For maximum efficiency and reliability, it is important to have maximum gas volume transfer through the regenerator. In order that this may be attained, it is important that the direction of gas flow be reversed when the displacer is at top dead center or bottom dead center.
In the prior art, the ports or holes in the spool valve are all of the same diameter and positioned so that their centers all lie on a plane perpendicular to the center line of the sleeve bearing. That arrangement of the ports provides for a fast opening valve with very high mass flow at the start of pressurization, since the pressure difference between the high pressure and low pressure is at a maximum just before the valve opens. The high mass flow rate produces a large pressure difference across the regenerator matrix as the fluid passes through it. A large pressure drop in the regenerator manifests itself in large mechanical loads on the displacer drive system and introduces losses due to fluid friction. The dwell time of the fluid within the regenerator matrix is decreased, which can result in reducing the heat transferred between the matrix and the fluid. The present invention is directed to a solution of that problem of uneven mass flow to and from the displacer.